This invention relates to a battery state monitoring apparatus for monitoring the remaining life of a battery of the type used by being repeatedly charged and discharged.
Batteries used while repeatedly undergoing charging and discharging find many applications and are essential in automotive vehicles. In a device or machine which employs such a battery, it is important to know the remaining life of the battery. The reason for this is that knowing the remaining life of the battery makes it possible to accurately determine when the battery should be replaced, the amount of use and when the changeover should be made between charging and discharging.
A specific example applying such art will now be described.
The applicant has previously filed applications relating to a vehicle equipped with a motor in which the front or rear set of wheels is driven by an engine and the other set is driven by a motor (see Japanese Patent Application Nos. 62-25735 and 62-37183). For example, in accordance with these previously filed applications, as shown in FIG. 15, an engine and a transmission 60 are mounted on the front-wheel side to drive the front wheels by the engine, and a motor 61, motor transmission 62 and battery 63 are mounted on the rear-wheel side to drive the rear wheels by the motor 61, with a road surface sensor 64 being mounted on the lower part of a front bumper. According to Japanese Patent Application No. 62-25735, driving force threshold values of the front and rear wheels are found by the road surface sensor 64, and driving force request values are apportioned to the engine and motor in dependence upon the remaining life of the battery 63 within a range in which the threshold values will not be exceeded. According to Japanese Patent Application No. 62-37183, such operating conditions as the accelerator opening, vehicle velocity and shift lever state are detected, the apportioned values of driving force of the engine and motor are set based on the operating conditions, and the apportioned values are revised in dependence upon the remaining life of the battery to control the engine and motor driving force.
Thus, monitoring the state of the battery is important. In the prior art, however, the state of the battery is monitored merely by measuring the terminal voltage of the battery or, in the case of a lead storage battery, by measuring the the specific weight of the electrolyte.
However, as will be understood from a plot of discharge duration time vs. battery voltage shown in FIG. 16, battery terminal voltage differs depending upon how much discharge current flows, even for the case of a single cell. Also, as shown in FIG. 17, there is a phenomenon in which, after discharge, terminal voltage fluctuates while the specific weight of electrolyte is stable. This means that the state of the battery cannot be accurately determined based solely on the terminal voltage.
Further, as shown in FIG. 17, a certain period of time is required for the specific weight of the electrolyte to stabilize. Consequently, the remaining life of the battery cannot be correctly determined in prompt fashion based solely on the specific weight of the electrolyte.